Any news if the cowls have been found yet? Typically they come off on rotation or shortly after take off if not all the latches are done up.
As for looking on a walkround, it's easily missed if one latch is done up and not the rest.
Airbus really need to concentrate on either a secondary locking system or some sort of indicator that is visible at eye level. The numbers of cowl loss alone shows this is a problem that needs to be engineered out to prevent it happening again.
Procedures and paperwork wont do it unless they are rigidly followed and still allow for human error.